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Barron Heating AC Electrical & Plumbing Blog

HVAC Helper – A Glossary for Homeowners


A glossary for homeowners or business-owners thinking about heating, air conditioning, and home performance

AFUE (Annual Fuel Utilization Efficiency) – AFUE is the rated efficiency of a combustion furnace. For example, a 95% AFUE model loses 5% of its produced heat up the chimney. In other words, $1 of fuel combusted in an 80% AFUE model loses $0.20 before it even enters the ducts.

Condensate (Condensation) – Heat pumps, air conditioners, and modern furnaces produce condensation and the removal of this collected water is always considered in system design.

Cold Air Return – The “cold air return” is the intake side (sucking side) of a duct system. This duct pulls air from the home and feeds it to the furnace to be reheated for distribution. Leaks in the return air duct are very important to seal as they allow material to be pulled in from wherever they lead (attics, crawlspaces, etc.). Unducted wall cavities are not acceptable for cold air returns in the modern HVAC world, as they are known to reduce efficiency and cause health safety issues.

COP (Coefficient of Performance) – This is an efficiency rating system that compares the output of heat to the consumption of electricity. An electric baseboard or electric furnace (aka resistance heat source) has a COP of 1.0, which means that for every unit of electricity that goes in, you get one unit of heat energy out. A heat pump may have a COP of 3.0- for every unit of electricity that goes in, you get three units of heat energy out.
$1 of heat with a baseboard heater = $3 of heat with a Heat Pump (3.0 COP)

Ducted Filtration and Furnace Filters – Filters located on either the furnace or grille end of the intake duct protect the furnace components from the build-up of airborne particles. More advanced filtration systems can be effective at cleaning the air in a home, but only if the duct and house leakage has been addressed. Filters are rated on the “MERV” scale based on how small of particles they are able to remove from the air stream.

**The Supply Duct Filters available at hardware stores are not recommended. They will negatively affect efficiency and air quality, as well as damage equipment.

Duct Sealing – According to extensive nationwide studies, duct leakage is a leading cause of wasted energy, poor indoor air quality, excessive dust, and comfort complaints. A study by the U.S. Department of Energy found that the typical duct system loses between 25% and 40% of its paid-for heat! Leaks are repaired with either hand applied material or a more comprehensive internal seal using an aerosol dispersed polymer (

Duct Sizing – Proper duct sizing is of absolute importance in effectively delivering conditioned air to the home. Improper duct sizing can lower the efficiency of the system, limit distribution (affecting comfort), and cause unnecessary ware on equipment.

Electric Resistance Heat – Think “toaster”. Baseboard heaters, wall heaters and electric furnaces are all forms of electric resistance heat technology and produce heat by passing electricity through a material that causes “resistance,” heats up and then radiates that heat either into an air stream or directly into a room. This is a very inefficient form of heating by modern standards and is going the way of the dodo as a primary heating source in most situations.

Fan Motors – There are two types of fan motors in the world of furnaces:

ECM (Electronically Commutated Motor) – These are variable speed motors that can ramp up and down depending on the call from the thermostat or furnace.

PSC (Permanent Split Capacitor) – These are single speed motors that are on or off.

Heat Pump (Ductless Mini Split) – Ductless Heat Pumps are the world’s most popular heating system. For most standard application, they are the most efficient and cost effective to install. For this reason, utility companies offer significant incentives to upgrade. This is a zonal heating system that operates on a refrigerant technology (see “Heat Pump” below). They do not utilize a duct system to distribute conditioned air.

Heat Pump (Forced Air) – Heat Pumps are really just an air conditioner that can go in reverse. In addition to the cooling process, these have the ability take the heat from the outdoor air and transfer it to the inside of your home. When the heat bearing refrigerant enters the “coil” at the furnace, the heat is picked up in the air stream and distributed into the home. This technology is significantly more efficient at creating heat than propane or electric resistance and even more efficient than natural gas.

Home Performance (AKA, Building Science) – Home Performance refers to the understanding that the whole house as a system and each component affects all others. For example: leaks in the ductwork will worsen indoor air quality, raise utility bills, cause drafts, shorten the lifespan of the furnace, and negatively affect health; air leaks to the attic through recessed lighting will do all the same things; both together will affect those things, but even more so. Because of these relationships, understanding your home’s performance through diagnostic testing is recommended by the US Department of Energy, Energy Star, and Consumer Reports before making any investment in heating, cooling, energy efficiency, or home health upgrades.

HSPF (Heating Season Performance Factor) – HSPF is the standard rating system for Heat Pumps. This is a rating given by regulatory agencies to compare the efficiency at which the heat pump operates to that of other  heat pumps.

Indoor Air Quality (IAQ) – “Indoor air quality” refers to the potential impact of your home’s air on occupant health and comfort. IAQ is judged on the presence of humidity, dust, radon gas, mold, fiberglass particulate, carbon monoxide and many other conditions. IAQ should be considered a high priority as it will affect both the long and short term health of occupants. Poor IAQ can exacerbate or cause: asthma, sinus infections, chronic respiratory ailments, eczema, fatigue, headaches, and many other issues.

Refrigerant – Refrigerant is the substance used in air conditioning and heat pump systems to transfer heat between the interior and exterior of the home. The refrigerant is transported in copper tubing between the indoor and outdoor coils. When the refrigerant is pressurized it absorbs heat from the air around it.

Registers (aka Grilles) – Registers, grilles, diffusers, and grates are all basically the same thing. In the industry they are commonly referred to as “grilles” or “diffusers.”

SEER (Seasonal Energy Efficiency Ratio) – SEER is the standard rating system for air conditioners. This is a rating given by regulatory agencies to compare the efficiency at which the air conditioner operates.

Static Pressure – Static pressure is the outward pressure of a substance against its container. In this industry we are concerned most often with the static pressure of the air in the duct system. Good static pressure allows for even distribution throughout the home, efficient removal of heat from the furnace’s heat exchanger or refrigerant coil, and less noise as the air ejects from the grille. Bad static pressure can exacerbate leakage, damage heating equipment, and significantly lower efficiency.

Supply Air – “Supply air” ducting is the delivery system for conditioned air- warm or cool. Supply air ducts should always be well sealed as any air that is lost out these pressurized ducts is lost to the outside, even when it is in a wall or floor cavity.

For more information, call or email your Home Performance Experts and set up a Home Performance Assessment!

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